Hold on...this shape looks familiar...is this the Long Tail of conversation and relationships?
I found this chart in the paper 'Using Rhythms of Relationships to Understand Email Archives', by the HCI Lab of the University of Maryland (via SmartMobs).
"Historians and social scientists believe that email archives are important artifacts for understanding the individuals and communities they represent. In order to understand the conversations evidenced in an archive, context is needed. In this paper, we present a new way to gain this necessary context: analyzing the temporal rhythms of social relationships. We provide methods for constructing meaningful rhythms from the email headers by identifying relationships and interpreting their attributes.
With these visualization techniques, email archive explorers can uncover insights that may have been otherwise hidden in the archive. We apply our methods to an individual’s fifteen-year email archive, which consists of about 45,000 messages and over 4,000 relationships."